In Hyun Nam

Biotransformation of 1,2,3-tri- and 1,2,3,4,7,8-hexachlorodibenzo-p- dioxin by Sphingomonas wittichii strain RW1

ABSTRACT Sphingomonas wittichii RW1 is able to catabolize 1,2,3,4-tetrachlorodibenzo-p-dioxin (H. B. Hong, Y. S. Chang, I. H. Nam, P. Fortnagel, and S. Schmidt, Appl. Environ. Microbiol. 68:2584-2588, 2002). Here we demonstrate the aerobic bacterial catabolism of the ubiquitous toxic diaryl ether pollutant 1,2,3,4,7,8-hexachlorodibenzo-p-dioxin by this strain. The products of this biotransformation were identified as tetrachlorocatechol and 2-methoxy-3,4,5,6-tetrachlorophenol by comparing mass spectra recorded before and after n-butylboronate and N,O-bis(trimethylsilyl)-trifluoroacetamide derivatization with those of authentic compounds. Additional experiments showed that the less-chlorinated 1,2,3,7,8-pentachlorodibenzo-p-dioxin was not transformed by the strain RW1. The importance of substitution patterns for the degradability of individual congeners was illustrated by the fact that the 1,2,3-trichlorodibenzo-p-dioxin was catabolized to yield 3,4,5-trichlorocatechol, whereas the 2,3,7-trichlorodibenzo-p-dioxin was not attacked.

Bioremediation of PCDD/Fs-contaminated municipal solid waste incinerator fly ash by a potent microbial biocatalyst.

Removal of polychlorinated dibenzo-p-dioxins and dibenzofurans (PCDD/Fs) from fly ash poses a serious problem. In the study presented here, we used a microbial biocatalyst which is a mixture of 4 bacterial and 5 fungal dioxin-degrading strains. The ability of this biocatalyst to bioremediate PCDD/Fs from contaminated municipal solid waste incinerator (MSWI) fly ash was examined by solid-state fermentation under laboratory conditions. Treatment of MSWI fly ash with the microbial biocatalyst for 21 days resulted in a 68.7% reduction in total toxic PCDD/Fs. Further analyses revealed that the microbial biocatalyst also removed 66.8% of the 2,3,7,8-substituted congeners from the fly ash. During the treatment period, the presence of the individual strains composing the microbial biocatalyst was monitored by the amplification of strain-specific DNA sequences followed by denaturing gradient gel electrophoresis (DGGE). This analysis showed that all of the bacterial and fungal strains composing this dioxin-degrading microbial mixture maintained under the dioxin treatment conditions. These results demonstrate that this microbial biocatalyst could potentially be used in the bioremediation of PCDD/Fs from contaminated fly ash.

Biodegradation of dibenzo-p-dioxin, dibenzofuran, and chlorodibenzo-p-dioxins by Pseudomonas veronii PH-03

The dioxin-degrading strain Pseudomonas veronii PH-03 was isolated from contaminated soil by selective enrichment techniques. Strain PH-03 grew on dibenzo-p-dioxin and dibenzofuran as a sole carbon source. Further, 1-chlorodibenzo-p-dioxin, 2-chlorodibenzo-p-dioxin and other dioxin metabolites, salicylic acid, and catechol were also metabolized well. Resting cells of strain PH-03 transformed dibenzo-p-dioxin, dibenzofuran, 2,2′,3-trihydroxybiphenyl, and some chlorodioxins to their corresponding metabolic intermediates such as catechol, salicylic acid, 2-hydroxy-(2-hydroxyphenoxy)-6-oxo-2,4-hexadienoic acid, and chlorocatechols. The formation of these metabolites was confirmed by comparison of gas chromatography–mass spectrometry (GC–MS) data with those of authentic compounds. Although we did observe the production of 3,4,5,6-tetrachlorocatechol (3,4,5,6-TECC) from 1,2,3,4-tetrachlorodibenzo-p-dioxin (1,2,3,4-TCDD) with resting cell suspensions of PH-03, growth of strain PH-03 in the presence of 1,2,3,4-TCDD was poor. This result suggests that strain PH-03 is unable to utilize 3,4,5,6-TECC, even at very low concentration (0.01 mM) due to its toxicity. In cell-free extracts of DF-grown cells, 2,2′,3-trihydroxybiphenyl dioxygenase, 2-hydroxy-6-oxo-6-phenyl-2,4-hexadienoic acid hydrolase, and catechol-2,3-dioxygense activities were detected. Moreover, the activities of meta-pyrocatechase and 2,2′,3-trihydroxybiphenyl dioxygenase from the crude cell-free extracts were inhibited by 3-chlorocatechol. However, no inhibition was observed in intact cells when 3-chlorocatechol was formed as intermediate.

A catabolic activity of Sphingomonas wittichii RW1 in the biotransformation of carbazole

The well-known bacterium Sphingomonas wittichii RW1 catabolically degrades dibenzo-p-dioxin and dibenzofuran, as well as their chlorinated derivatives. The catabolic degradation of dioxin is initiated by a ring-hydroxylating dioxygenase. The biotransformation of carbazole by S. wittichii RW1 was determined in the present study. Dioxin dioxygenase from the dibenzofuran induced RW1 strain was thought to be unable to attack carbazole, which includes a heterocyclic aromatic dibenzopyrrole system. However, our results showed that carbazole was transformed to anthranilic acid and catechol. The color of the culture suspension changed upon addition of carbazole due to formation of a nitrogen-containing metabolite. Relevant metabolic intermediates were identified by gas chromatographic mass spectrometry and electrospray ionization time-of-flight mass spectrometry with comparison to the corresponding authentic compounds. The dioxygenase of the dibenzofuran induced RW1 attacked at the angular position adjacent to the nitrogen atom to give a dihydroxylated metabolic intermediate. Contrary to predictions made in previous reports, S. wittichii RW1 displayed positive catabolic activity toward carbazole.